Chromosomal Polymorphism of Mandarin Vole, Microtus Mandarinus (Rodentia) J

http://www.paper.edu.cn Hereditas 138: 47–53 (2003) Chromosomal polymorphism of mandarin vole, Microtus mandarinus (Rodentia) J. X. WANG1, X. F. ZHAO1, Y. DENG1,H.Y.QI1 and Z. J. WANG2 1School of Life Sciences, Shandong Uni6ersity, Jinan, P. R. China 2Plant Protection Center of Shandong Pro6ince, P. R. China Wang, J. X., Zhao, X. F., Deng, Y., Qi, H. Y. and Wang, Z. J. 2003. Chromosomal polymorphism of mandarin vole, Microtus mandarinus (Rodentia). — Hereditas 138: 47–53. Lund, Sweden. ISSN 0018-0661. Received May 8, 2002. Accepted January 21, 2003 The mitotic and meiotic chromosomes of mandarin vole, Microtus mandarinus Milne-Edwards, from Shandong Province of China were analyzed by conventional, G- and C-banding and Silver-staining techniques. We detected chromosomal polymorphism in the vole, exhibiting diploid chromosome numbers 2n=48–50 and variable morphology of the 1st pair, one medium sized telocentric pair and the X chromosomes. Four types of karyotypes were revealed in the population. According to banding analysis, there were pericentric inversion, Robertsonian fusion and translocation in M. mandarinus karyotype evolution. The X displayed two different morphologies, which could be explained by prericentric inversion and a telocentric autosome translocation. Jin-Xing Wang, Department of Biology, School of Life Sciences, Shandong Uni6ersity, Jinan 250100, Shandong, P. R. China. E-mail: [email protected] The small-sized subterranean rodent, mandarin vole, Cytological methods Microtus mandarinus (Milne-Edwards, 1871) is one of Each specimen was injected intraperitoneally with the harmful mice to farming, forestry and horticul- 1–2 mg colchicine per gram of animal 2 to 3 hours ture when its populations are high. It may cause prior to dissection. Bone-marrow cells were rinsed damage to fruit orchards, especially during winter, by out from femur and humerus, hypotonized in 0.075 eating the bark from the roots and lower trunks of mol/l. KCl for 35 min at 30°C, and subsequently trees (WANG and XU 1992). fixed with Carnoy’s solution (methanol:acetic acid, The mandarin vole is widely distributed in north- 3:1). Chromosome preparations were made by a stan- central Mongolia and adjacent part of Siberia south dard air-drying method. Chromosomal classification of Lake Baikal, China and Korea (NOWAK and followed LEVAN et al. (1964). PARADISO 1983). In China, it is common in Testes were dissected out from males and connec- Shanxi, Shaanxi, Inner Mongolia, Henan, Hebei, An- tive tissue was removed. They were then transferred hui, North Jiangsu and Northeast China (HONACKI to 0.075 mol/l KCl, homogenized, and incubated for et al. 1982; WANG and XU 1992). ZHU et al. (1993) 30 min at 30°C. Fixation and chromosome prepara- studied cytogenetically the species from Lingbao tion were the same as for bone marrow cells. County, Henan Province, China. M. mandarinus, Differentially stained chromosomes were prepared was first recorded in Wendeng, Shandong Province by the trypsin method for GTG-banding (SEABRIGHT of China in 1995. After cytogenetic investigation 1971) and BSG method for C-band (SUMNER 1972). of specimens from Shandong population, we found Nucleolar organizing regions (NORs) were silver variations in diploid number and chromosome poly- stained according to the protocol of HOWELL and morphism distinct from those of the Henan popula- BLACK (1980). tion. MATERIAL AND METHODS RESULTS Animals Diploid number and chromosomal polymorphism Twelve individuals (eight males and four females) of Chromosome numbers from 12 individuals were de- Microtus mandarinus were collected at Zhangjiachan, termined (Table 1). The chromosome numbers Wendeng city, Shandong Province, China during ranged from 48 to 50. Nine individuals (No. 1–7 1996–1998. and 9–10) displayed a diploid number of 49, one 转载中国科技论文在线 http://www.paper.edu.cn 48 J. X. Wang et al. Hereditas 138 (2003) Table 1. Chromosome count of Microtus mandarinus No. of Sex Number of chromosome/ No. of cells Diploid Morphology Sex Karyotype specimens cell analysed number of 1st Pair chromosome 47 48 49 50 51 1 M 3 9 48 3 63 49 st st Xst Y* I 2sF 2 5 40 4 1 52 49 tstXst Xm I 3 M41 4 32 2 39 9ststXst YI 47M 3414249ststXst YI 5sM 5 40 3 48 49 tstXst YI 6sF4248 50 9tstXst Xm I 74F 4515049ststXst Xm I 8 F 3 53 4 60 48 st st Xst Xm II 9sM41 2 23 26 9ttXst Y III 10 M 3 36 1 40 49 st t Xst Y III 11 M 4840153 50 st t Xm YIV 12 Ms1345150 50 ttXm YIV *Xm and Xst indicated that the X was a metacentric (m) or subtelocentric (st) chromosome respectively. showed 2n=48 (No. 8) and two, 2n=50 (No. 11– Type II: One individual had a 2n=48 karyotype 12). Among those specimens 2n=49, all individuals (Fig. 1C). There is also a large subtelocentric, one had 23 pairs of autosomes and one additional un- medium sized submetacentric, and an unpaired small paired small autosome; and the sex chromosomes telocentric, but this type differs from type I in that were XX(female)/XY(male). there are 20 telocentric pairs which decrease gradu- Polymorphism was detected in the morphology of ally in size, and a large unpaired metacentric which the first pair of autosomes and the X chromosome. may have been derived by fusion of two medium The first pair of autosomes showed two morphologies: sized telocentrics. The X chromosomes are morpho- m st two subtelocentrics or a subtelocentric and a telocen- logically similar to those of the type I (X and X )in tric (Fig. 1A–E). Two types of large sized X chromo- female. The fundamental number of type II is the somes were recognized in the species: a subtelocentric same as that of Type I (FN=51). X(Xst), the largest element in all karyotypes, and a Type III: The karyotype of individuals No. 9–10 metacentric X (Xm), the second large element in consist of 2n=49 chromosomes (Fig. 1D). All chro- female karyotypes. The Xst is much longer (about 13 mosomal elements are the same as those of type I %) than Xm in relative length. It means that Xm may except for the first pair of autosomes which consist of a large telocentric and a large subtelocentric chromo- experience structural rearrangements such as autoso- some. The telocentric is approximately of the same mal translocation, partial deletion, excessive duplica- length as the subtelocentric. This type also has the tion of C-heterochromatin and produced Xst.For same fundamental number (FN=51) as type I. most male voles, the X chromosome was a large Type IV: Individuals (No. 11–12) had a 2n=50 subtelocentric chromosome (Xst) and the Y chromo- karyotype (Fig. 1E). Comparing with the former some was a small telocentric chromosome (Fig. 1A types, the first pair of autosomes is the same as type and D). But the X chromosome detected in two male m III (st, t), there is also one submetacentric pair, but individuals was a metacentric chromosome (X ) (Fig. 22 telocentric pairs, and no unpaired telocentric auto- 1E). some. The X chromosome in the male is a large sized We deduced four kinds of karyotypes out of the metacentric (Xm) which is different from the other comparison of the 12 individuals studied: types, subtelocentric (Xst), in males. The fundamental Type I: The karyotype of 7 individuals revealed number of chromosomes of this type is 52. 2n=49 (Fig. 1A and B). This complement is charac- As a whole, it can be concluded that the karyotypic terized by one large subtelocentric, one medium sub- polymorphisms found involves the X chromosome, metacentric and 21 telocentric autosomal pairs which the first pair of autosomes, the fusion of two medium decrease gradually in size and one additional single sized telocentrics and the existence or absence of an small telocentric autosome. The X chromosome is the unpaired small autosome. largest subtelocentric element while the Y is a small C-banding patterns sized telocentric (Fig. 1A). In the female studied by us, the sex chromosomes consist of Xst and Xm (Fig. 1B). Centromeric C-bands were found in all autosomes The fundamental number (FN) of chromosomes is 51. excluding 3–4 pairs of autosomes. The X chromo- 中国科技论文在线 http://www.paper.edu.cn Hereditas 138 (2003) Chromosomal polymorphism of mandarin 6ole 49 Fig. 1. 中国科技论文在线 http://www.paper.edu.cn 50 J. X. Wang et al. Hereditas 138 (2003) Fig. 1A–E. Conventional (A–E) and banding karyotypes (F–H) of M. mandarinus. A,2n=49, male; B,2n=49, female; C,2n=48, female; D,2n=49, male; E,2n=50, male; F. C-banding karyotype; G, G-banding pattern; H. Silver staining pattern, 1 shows 8 NORs, and 2 shows 7 NORs. 中国科技论文在线 http://www.paper.edu.cn Hereditas 138 (2003) Chromosomal polymorphism of mandarin 6ole 51 some bears large pericentromeric heterochromatin blocks; Y chromosome is entirely heterochromatic and intensely stained (Fig. 1F). Ag-NORs banding patterns A varying number of Ag-NORs was detected in M. mandarinus. These ranged from 2 to 8 in different metaphases and individuals. Usually, silver-stained NORs were found on the telomeric end of the long arm of pair No. 1, and 3 pairs of medium and small telocentrics that were not morphologically further specified (Fig. 1H). G-banding patterns GTG banding pattern provided the precise identifica- tion of the majority of the chromosomal pairs (Fig. 1G). The bands of the first pair of autosomes are identical in st, st pair. From the characteristic banding patterns, the relationship of the two autosomes can be explained by pericentric inversion. From the banding patterns of two types of X chromosomes, we can postulate that the original type of X was a large Fig.

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